Access door



H. E. OHMAN Aug. 14, 1956 ACCESS DOOR 2 Sheets-Sheet l Filed April 23. 1953 ATTORNEY 1956 H. E. OHMAN 2,758,554

ACCESS DOOR Filed April 25, 1953 2 Sheets-Sheet 2 INVENTOR HAM: E. OHMAN ATTORNEY Urited States Parent O r A'CCESS DO'OR Hans E. Ohman, Worcester, Mass., assignor to Riley 'Stoker Corporation, Worcester, Mass., a Corporation of Massachusetts Application April 23 1953, 'Serial No. 350,(328

` 5 Claims. (Cl. 110-179 usual negative draft furnace, there are some problems to be overcome in constructing such a furnace. One of these problems is the provision of a safe access door through which the operator can observe the furnace performance and through which lances and other implements may be inserted. It is evident, of course, because of the positive pressure in the furnace that opening a door in the wall thereof will cause a violent stream of hot gases or flame to pass outwardly. Eurthermore, in the usual furnace the gas pressure is subject to pulsation? so that the gas pressure at a given time may become momentarly quite high. For that reason it is necessary to provide these furnaces With an access door which will provide for all contingencies and which will be perfectly safe despite possible carelessness on the part of the operator. The present invention involves such a door having a novel and practical Construction.

It is therefore an outstanding object of this invention to provide a practical and inexpensive access door for a pressun'zed furnace.

It is another object of the invention to provide an ;access door which cannot be opened until provision has been made for preventing passage of hot gases or flame outwardly through the opening. i

It is a further object of the present invention to provide an access door-having air ,flow means for assuring that gases in the pressure furnace do not pass outwardly through the opening and having a novel and practical i interlock between a valve regulating the air flow and a latch maintaining the door in closed position.

' v To the accomplishment of the foregoing and related ends,; the invention, then, comprises the features hereinafter fully described and particularly ponted out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however,

, of but a -few of the various ways in which the principle of the invention may be employed..

In said annexed drawings:

- -Figure 1 is a horizontal sectional view of the wall of a. pressurized furnace showing 'an access door ernbodying the present invention,

V Figure 2 is an `elevational view of the invention,

I `-l-"igure 3 is an enlarged elevational view of a latch `:mechanism forming a part of the invention in a different position of operation than that indicated' in Figure 2,

. and

- Figure 4 is a horizontal sectional view of the latch of v Figure 3 taken on the line 4-4 thereof.

Like reference characters denote similar parts in the eral aspects of the invention, the access door, indicated generally by the reference numeral 10, is shown in place in a furnace wall 11 having water wall tubes 12 one of which is bent laterally and inwardly to leave a space for an opening 13. The opening 13 is formed from the refractory of the furnace wall and is of frusto-conical conformation converging inwardly of the furnace. A door frame 14 of somewhat annular shape surrounds the outer edge of the opening 13 and is of hollow Construction to provide an annular air chamber 15. Threaded openings 16 extend from the air chamber 15 through the wall of the door frame 14 in the direction of the furnace and in these openings are screwed air nozzles 17. There are a considerable number of these air nozzles arranged in a circle on the furnace side of the door frame 14 and the axes of the nozzles define a conical surface having an included angle of about 32 degrees, the apex of which is somewhat inside the fur-mace. The included angle of the conical surface of the opening 13 is somewhat smaller than that of the cone defined by the axes of the air nozzles.

On the outer surface of the door frame 14 and surrounding a circular opening therethrough is a circular groove 18 in which resides a scaling pad 19. A circular plate 20 overlies the door frame 14 and is provided with an inwardly extending fiange 21 which presses against the scaling pad 19. Extending inwardly from the inner surface of the plate 20 is a frusto-conical flange 22 of relatively thin wall section. The flange 22 converges inwardly of the furnace and is filled with a refractory material 23. The size and relationship of the fiange 22 is such that when the flange 21 is resting against the scaling pad 19, the surface of the flange 22 engages the corner of the opening through the door frame 14. A bifurcated connecting member 24 extends outwardly from the plate 26 and is provided with a vertical pin 25. An elongated latching bar 26 has its intermediate portion residing between the bifurcations of the connecting member 24 with the vertical pin 25 extending therethrough for pivotal movement. A handle 2'7 of the usual type is fastened to the bar 26 and hangs downwardly therefrom. One end of the latching bar 26 is pivotally connected to a hinge 28 fastened to the side of the door frame 14. The hinge 28 has a hinge pin 29 which passes through the latching bar to permit pivotal movement thereof.

The other end of the latching bar 26 is provided With a camming surface 30 which is slightly inclined to the vertical and which is adapted to engage a latch pin 31. The latch pin 31 has a cylindrical portion 32 which resides in a bore 33 extendng inwardly of a boss 34 extending outwardly from the door frame 14. The inner end of the pin 31 is provided with a flange 35 engaged by a compression spring 36 which in turn is held in place by a threaded plug 37 threaded into the outer portion of the bore 33. The plug is provided with wrench lugs 38 by which means its position may be adjusted. The

pin 31 is therefore normally biased inwardly or" the bore 33. The outer end of the pin 31 is generally semicylindrical in shape and Would presumably be formed by starting with a pin having an overall dimension similar to the cylindrical portion 32 and milling away slightly less than all the material on one side of a cutotf plane parallel and spaced slightly from a diametral plane. Adjacent the intersection of the cylindrical portion 32 and the outer semicylindrical portion of the pin 31 is a notch 39 extending inwardly from one edge thereof. The notch 39 has a beveled edge adjacent the cutofr plane of the outer portion of the pin 31. The extreme outer end of the pin 31 is provided with a reduced portion 40 of square cross-section. The reduced portion loi; to`insert cleaning tools, he must first turn %m m t b cntfi tit n l i ?t the `cylindrical portions of the outer portion of the pin, one surface of the reduced portion being defined by the cutoff plane `of the outer portion. A notch 41,*best`shown in Figure 4, extends inwardly from the edge of the semi-cylindrical portion of the pin opposite the edge from which the notch 39 extends. e

p A plug valve 42 is mounted to one side and outwardly of the door frame 14. This valve is connected to a source of air pressure, not shown, and also is connected to the air chamber 15. The valve is provided with a square actuating handle 43 such that the valve is intended to {be normally opened and closed with a wrench. On this atuating 'handle 43 is mounted a guard 4.4. This guard has an inner plate member 45, through which the handle 43 extends. The member! 45 has the shape of a circular scgment The valve 42, the guard 44,` and the pin 31 are so shaped andiarranged that the member 45 may extend into the notch 41 on occasion. The guard `44 is also provided with a shielding portion 46 which is spaced from theplate member 45 and overlies the pin, 31 on occasion. The valve 42 is mounted and attched to the door frame 14 by means of a bracket 47 shown in Figure 2. In Figura 2 is also shown a pipe 4& connecting the valve 42 to the air chamber 15. The guard 44 is also providedwith an actuating handle 49. The operation of the invention will now be understood in iew of the above description. During normal operation the furnace will be fired with a positive pressrebmaintained therein so that a similar pressure rnust necessarily exist in the opening 13 through the fyrnacewall 11. Withthe access door closed, the plate 2 0 is p ressed against the door frame 14 with the flange 21 hearing against the scaling pad 19 and with the trustoconical flange 23 engaging theopening through the door frame The surface 30 of the `unhinged end of the l atcihing bar 26 resides in the notch 39 of the pin 31. Since the spring 36 biases the pin inwardly, the bar 26 'will be held inwardly, ths pressing the plate firmly against the seal 19 through the pin 25 and the connecting member 24. When the operator wishes to open the accssdoor to observe the conditions in the furnace the actuating handle 43 of the valve 42 to open the valve and to admit air under pressure into the chamber 15. When ai; isbnilt up in the air chamber 15, it, of course, esapesthrough the nozzles 17 causinga flow of airinto the turrace through the opening 13 and producing a drop in pressure through the opening. This assures that the gases and fiame in the furnace do not pass outwardly through the'opening 13. The valve may be actated by grasping the actuating handle 49 of the guard '44, if so des ired, or a wrench may be directly inserted on the actuating handle 43 of the valve 42. Once the valve 42 has been opened; and air is flowng through the nozzles 17, safeguarding the operator when the dooris opened, the'gperator may then place a wrench on the reduced portion 40 of the pin 31. By the turning of the pin, the free end of the bar26 finds itself residing adjacent It is no :the cutoff plane of the outer end of the pin.

longer lying in the notch 39 and is no longer restricted against outward movement. The operator then grasps the handle 27 pulling outwardly, the bar 26 pivots about its hinge pin '29, and carries with it theplate 20 and all accessory equipment. These members 'are swungyto the side of the opening and the operator is free to observe the fur-hace or to work through the access opening.

When he wishes to close the door, he swings the bar 26 about its hinge so that the fiange 21 of the 'plate '20 rcsides against the seal 19, at which time the free end of the bar 26 resides adjacent the pin 31 He then places a wrench on the reduced portion 40 and, by t rning the pin, the` camming surface 30 cams ?along the bveled portion of the notch 39 and the bar is drawn `i`r`wardly"toward the frnace. The sifuation is maintained through the pressure of the spring 36, the free end of the bar residiig in the notch 39 and being 'held therein. The position of the elements shown in Figures l and 2 is that which exists when the door is free to open. It is to be noted that at that time the free end of the bar 26 resides adjacentthe cutott plane of the outer portion of the pin 31 and 'also resides outside of the notch 39. The door is free to open. At that time the sheld 46 of the guard 44 resides in an upper position away front the reduced portion `40 of the pin. That is to say, the operator is 'permitted to 'put 'a wrench on the reduced portion 40 which would not 'be possible if the sheld 46 were overlying the pin. In Figures 3 and 4 is shown the condition of the latching elements when the access door is closed. At that 'time it will be noted that the sheld 46 overles the reduced portion 40 of the pin 31 so that it is not possible to place a wrench thereon to open the door. At the same time, as *is best seen in Figure 4, a circular segmental portion'of the plate member of the guard 44 resides'in the notch 41 with 'the outer portions 'residing close to the 'end surface of the notch. "In this position any attempt to turn the `pin 31 will result in 'the end surface of the notch 41 jamming 'against the plate member 45 so 'that the pin will not turn. In 'other words it is not possible to turn the pin 31 unless the valvehas been turned to its open position at which time the 'plate member 45 does not'reside in .the notch 41 and the sheld 46 does not overle the reduced portion 40 of the pin '31. `It is, therefore, not possible 'to open the 'door without the safeguard of air passing through'thc nozzles *17.

Other modes of applying the `principle of the invention may be employed, change being made -as 'regards the details described, provided the features stated in the `fol- 'lowing`claims, or the equivalent of such, be employed,

I `therefore'particularly point 'out and distinctly claim as my invention:

'1. Ah access door `forapressurized furnace co'mprising a door frame 'having an 'inner 'and an outer `side and having 'an opening 'therethrough, air 'nozzles surrounding the opening 'and directed inwardly for maintaining an air flow to counteract the furnace `pressure, a valve having a 'handle "and an extension theref for controlling 'the flow of air to the nozzles, a'plate adapted to reside in sealirg 'relation to 'the'opening and to 'be removed therefrom, 'a 'latching `'bar on *the intermediate portion 'of which the plate is niointed, the latching bar being hinged atone end adjacent the opening, and a pin engaged'by `thefreefend of the `latching 'bar'andby the extension of 'the valve' handle whe'n the'plt'e is in the said scaling relation, 'thepin looking the -bar and the valve so `that 'the plate c'annot be moved away from its 'scaling relation with the opening unless the valve is in 'stch a positin as to admit *air to the nozzles, the

of the furnace for maintaining an air'flow toc'ounteract the furnace pressure, a valvecontrollir'g the fiow of air to thenozzles, and 'having an actuating handle 'with an extension, a latching bar` having -one 'end' hinged adjaoent `furrate w'allg'a plate mounted on 'an intermediate por- -pen'dicular `to "the furnace*wall, "a first 'notch `formed in the pin and engaged bythe -free end*of`the latching bar when :the plate isin saidseling` position, :and a second notch engaged by the extension of the valve handle when it is in valve-closing position, so that the pin cannot be rotated to release the latching bar from the first notch unless the extension is in such a position that it is free from the second notch, the pin being capable of movement to engage the latching bar to lock the plate in the said sealng position when the extension of the valve handle is in valve-closing position.

3. An access door as recited in claim 2 wherein the outer end of the pin s fol-med for engagement by a Wrench, and the extension is provided with a shield which overles the said other end to prevent engagement by a Wrench when the valve is closed.

4. An access door as recited in claim 2 wherein the pin is resiliently biased to move longitudnally toward the furnace so that the plate is held in scaling relation 15 to the opening when the free end of the latching bar is held in the first notch.

5. An access door as recited in claim 2 wherein the portion of the extension which is adapted to lie in the second notch When the valve is closed includes a circular segment.

References Cited in the file of this patent UNITED STATES PATENTS 669,978 Brouhon Mar. 19, 1901 740,757 Hofmann Oct. 6, 1903 805,295 Hofmann Nov. 21, 1905 2,528,671 Selnik Nov. 7, 1950 2,545,886 Koostra Mar. 20, 1951 

